Leak diagnosis method and leak diagnosis device for blowby gas treatment device of internal combustion engine

ABSTRACT

A blowby gas treatment device includes a pressure control valve, a fresh air induction pipe, a first blowby gas pipe, a second blowby gas pipe, a shutoff valve, a one-way valve, and a PCV valve. A leak diagnosis includes a first-stage diagnosis to determine whether or not falling of a pressure in a crank case after closing of the shutoff valve under a non-supercharging condition is normal. A second-stage diagnosis is implemented by moving the pressure control valve from a fully opened state into a fully closed state, and determining whether an intake air quantity in each state is equal to each other. When the intake air quantity in each state is equal to each other, presence of an in-system leak is determined. When a fully closed state intake air quantity is different from a fully opened state intake air quantity, presence of an out-of-system leak is determined.

TECHNICAL FIELD

The present invention relates to a blowby gas treatment device of aninternal combustion engine for inducing blowby gas from a crank caseinto combustion chambers for treatment, and relates particularly to adevice for diagnosing presence or absence of gas leaking from piping ofthe blowby gas treatment device.

BACKGROUND ART

A typical blowby gas treatment device of an internal combustion engineis configured to induce fresh air into a crank case from an intakepassage or the like via a fresh air induction pipe, and induce the freshair and blowby gas from the crank case into the intake passage via ablowby gas pipe, and finally supplies the fresh air and blowby gas tocombustion chambers. A patent document 1 discloses a normal aspirationengine provided with no supercharging device, in which a tip end of ablowby gas pipe is connected to a section of an intake passagedownstream of a throttle valve so as to cause a flow of blowby gas bymeans of a negative pressure. A typical blowby gas pipe is provided witha PCV valve, wherein the PCV valve is configured to be opened by adifferential pressure between an inside of a crank case and an intakepassage (a downstream side of a throttle valve).

On the other hand, a patent document 2 discloses a blowby gas treatmentdevice suitable for a supercharging engine provided with a supercharger,in which in addition to a blowby gas pipe connected to a downstream sideof a throttle valve, a second blowby gas pipe is provided for inducingblowby gas from a crank case into an upstream side of a compressor whilesupercharging is active. This blowby gas treatment device includes afresh air induction pipe and the two blowby gas pipes, wherein each ofthe blowby gas pipes is provided with a one-way valve for preventing gasfrom inversely flowing.

If such a blowby gas treatment device undergoes a leak due to occurrenceof a hole in a pipe or detachment of a pipe, it is required toimmediately detect the leak and allow the leak to be recognized byturning on a warning light or so in order to prevent deleterious blowbygas from being released into an environment. Especially for a vehicularinternal combustion engine, it is required by regulations in manyregions to diagnose leaking from piping, and in response to anabnormality, turn on a warning light.

Patent document 1 discloses a leak diagnosis to close the fresh airinduction pipe temporarily for leak diagnosis, and monitor falling of apressure in the crank case after the closing of the fresh air inductionpipe. As induction of fresh air is stopped while the internal combustionengine is rotating, a negative pressure downstream of the throttle valveis applied to the inside of the crank case, so that without occurrenceof a hole in a pipe or detachment of a pipe, the pressure in the crankcase falls gradually. Accordingly, when the pressure fall in the crankcase is insufficient, presence of some leaking is determined.

However, if such a leak diagnosis method is applied to a superchargingengine and the leak diagnosis method is performed under a superchargingcondition, it is possible that a failure in a system of a blowby gastreatment device, which is not a leak in the strict sense, namely, not aleak to the outside of the system of the blowby gas treatment device, isdetected erroneously as a leak due to occurrence of a hole in a pipe ordetachment of a pipe. For example, when the one-way valve of the secondblowby gas pipe in patent document 2 is stuck in an open state, freshair inflows via the second blowby gas pipe so that the pressure fall inthe crank case may be insufficient.

The presence of an out-of-system leak due to occurrence of a hole in apipe or detachment of a pipe results in release of deleterious blowbygas to the environment, whereas an in-system failure such as open-statesticking of the one-way valve as described above does not result in anoutflow of blowby gas to the external environment. The two kinds ofleaks are different in seriousness, but it is impossible to distinguishthe two kinds of leaks from each other by applying a conventionaldiagnosis to a supercharging engine.

PRIOR ART DOCUMENT(S) Patent Document(s)

Patent Document 1: Japanese Patent Application Publication No.2018-44486

Patent Document 2: Japanese Patent Application Publication No.2010-511835

SUMMARY OF INVENTION

According to the present invention, a leak diagnosis method is presentedfor a blowby gas treatment device of an internal combustion engine,wherein the blowby gas treatment device includes: a fresh air inductionpipe structured to induce fresh air into a crank case from a section ofan intake passage downstream of an air flow meter; a pressure controlvalve disposed in a section of the intake passage upstream of a throttlevalve and upstream of a compressor; a first blowby gas pipe structuredto induce blowby gas from the crank case into a section of the intakepassage between the compressor and the pressure control valve; a secondblowby gas pipe structured to induce blowby gas from the crank case intoa section of the intake passage downstream of the compressor anddownstream of the throttle valve; a shutoff valve structured to blockthe fresh air induction pipe; a one-way valve structured to allow only agas flow in the first blowby gas pipe from the crank case to the intakepassage; and a PCV valve disposed in the second blowby gas pipe.

According to the present invention, the leak diagnosis method includes:performing a first diagnosis to close the shutoff valve under asupercharging condition and determine whether falling of a pressure inthe crank case after the closing of the shutoff valve is normal orabnormal; and performing a second diagnosis to control the pressurecontrol valve into an open-side state and a closed-side state under anon-supercharging condition and determine whether or not an open-sidestate intake air quantity is equal to a closed-side state intake airquantity, wherein the open-side state intake air quantity is a quantityof intake air measured when the pressure control valve is in theopen-side state, and wherein the closed-side state intake air quantityis a quantity of intake air measured when the pressure control valve isin the closed-side state.

The leak diagnosis method further includes: determining presence of aleak to an outside of a system of the blowby gas treatment device, inresponse to a condition that the first diagnosis determines the fallingof the pressure as abnormal and the second diagnosis determines theopen-side state intake air quantity as unequal to the closed-side stateintake air quantity; and determining presence of a failure within thesystem of the blowby gas treatment device, in response to a conditionthat the first diagnosis determines the falling of the pressure asabnormal and the second diagnosis determines the open-side state intakeair quantity as equal to the closed-side state intake air quantity.

In this way, according to the present invention, it is possible toidentify a leak to the outside of the system of the blowby gas treatmentdevice in which blowby gas flows out to the external environment, and afailure within the system of the blowby gas treatment device such as aleak through a valve, and allow those to be easily addressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram showing system configuration of ablowby gas treatment device provided with a leak diagnosis deviceaccording to an embodiment.

FIG. 2 is a flowchart showing a flow of processing of a leak diagnosis Aperformed under a non-supercharging condition.

FIG. 3 is a time chart showing behavior of pressure falling in a crankcase during a first stage of the leak diagnosis A.

FIG. 4 is a characteristic diagram showing a change in an intake airquantity during a second stage of the leak diagnosis A.

FIG. 5 is a flowchart showing a flow of processing of a leak diagnosis Bstarted under a supercharging condition.

FIG. 6 is a time chart showing behavior of pressure falling in the crankcase during a first stage of the leak diagnosis B.

FIG. 7 is a characteristic diagram showing a change in the intake airquantity during a second stage of the leak diagnosis B.

FIG. 8 is an explanatory diagram showing a gas flow when a pressurecontrol valve is fully closed during the second stage of the leakdiagnosis B.

MODE(S) FOR CARRYING OUT INVENTION

FIG. 1 shows system configuration of a blowby gas treatment device of aninternal combustion engine 1 and a leak diagnosis device according tothe present invention. The internal combustion engine 1 according tothis embodiment is a spark ignition engine provided with a turbochargeras a supercharger. In the internal combustion engine 1, gas containingan unburned component, namely, blowby gas, leaks from a combustionchamber 2 of each cylinder into a crank case 3. This blowby gas isinduced via a blowby gas passage 4 into a first oil separator chamber 6,wherein the blowby gas passage 4 is formed in the internal combustionengine 1 to extend in a vertical direction, and wherein the first oilseparator chamber 6 is formed in a top part of a cylinder head cover 5.The top part of the cylinder head cover 5 is formed with a second oilseparator chamber 7 in addition to the first oil separator chamber 6.The second oil separator chamber 7 communicates with a space in acylinder head, wherein the space communicates with the crank case 3.

The internal combustion engine 1 is provided with a crank case pressuresensor 8 that is located in a suitable position in the internalcombustion engine 1 and senses pressure in the crank case 3.

The internal combustion engine 1 includes an intake passage 11 having aninlet as an upstream end provided with an air cleaner 12 and includingan intermediate section provided with a compressor 13. A throttle valve14 is located downstream of the compressor 13 for controlling an intakeair quantity of the internal combustion engine 1. The throttle valve 14is an electronically controlled throttle valve whose opening iscontrolled by an engine controller 15, wherein the throttle valve 14includes an electric actuator such as an electric motor. An intercooler16 is disposed between the compressor 13 and the throttle valve 14 forcooling intake air compressed by the compressor 13. The throttle valve14 is located upstream of an intake collector 17. A plurality of intakebranch pipes 17 a are branched from the intake collector 17, whereineach intake branch pipe 17 a reaches a corresponding cylinder. Theintake collector 17 is provided with a boost pressure sensor 20 forsensing an intake pressure (boost pressure).

In a section of the intake passage 11 upstream of the compressor 13, apressure control valve 18 is provided for generating a negative pressurein a region between the pressure control valve 18 and the compressor 13.The pressure control valve 18 is a butterfly valve similar to thethrottle valve 14. In order to generate a negative pressure as requiredin accordance with an operating condition of the internal combustionengine 1, the opening of the pressure control valve 18 is controlled viaan electric actuator by the engine controller 15. For sensing the intakeair quantity of the internal combustion engine 1, an air flow meter 19is located upstream of the pressure control valve 18, namely, betweenthe pressure control valve 18 and the air cleaner 12. The air flow meter19 is a hot-wire air flow meter in this example, but may be of anothertype.

The blowby gas treatment device includes three pipes by external piping.Specifically, the pipes include a fresh air induction pipe 21, a firstblowby gas pipe 22, and a second blowby gas pipe 23, wherein the freshair induction pipe 21 induces fresh air into the crank case 3, whereinthe first blowby gas pipe 22 induces blowby gas into a section of theintake passage 11 upstream of the compressor 13, and wherein the secondblowby gas pipe 23 induces blowby gas into a section of the intakepassage 11 downstream of the throttle valve 14.

The fresh air induction pipe 21 includes: a first end connected to asection of the intake passage 11 upstream of the pressure control valve18, wherein the first end is an upstream end in terms of a flow of freshair; and a second end connected to the second oil separator chamber 7 ofthe internal combustion engine 1, wherein the second end is a downstreamend in terms of the flow of fresh air. A shutoff valve 24 is provided atthe upstream end of the fresh air induction pipe 21, namely, at aportion of the fresh air induction pipe 21 connected to the intakepassage 11, for blocking the fresh air induction pipe 21 for leakdiagnosis. The shutoff valve 24 is an on-off electromagnetic valve andis opened and closed by the engine controller 15. During normaloperation of the internal combustion engine 1, the shutoff valve 24 isin an open state allowing fresh air to be induced into the crank case 3via the fresh air induction pipe 21. The air flow meter 19 is locatedupstream of a portion of the intake passage 11 connected to the freshair induction pipe 21, and is structured to measure as an intake airquantity a flow rate of gas containing fresh air flowing into the freshair induction pipe 21.

The first blowby gas pipe 22 includes: a first end connected to thefirst oil separator chamber 6 of the internal combustion engine 1,wherein the first end is an upstream end in terms of a flow of blowbygas; and a second end connected to a section of the intake passage 11between the pressure control valve 18 and the compressor 13, wherein thesecond end is a downstream end in terms of the flow of blowby gas. Aone-way valve 25 is provided at a point of connection between the firstblowby gas pipe 22 and the first oil separator chamber 6, for allowingonly a gas flow from the crank case 3 (the first oil separator chamber6) to the intake passage 11. The one-way valve 25 is a mechanical checkvalve having a valve element that has a conical shape and is opened andclosed by a differential pressure in this example. The one-way valve 25prevents an inverse flow from the intake passage 11 to the crank case 3.

The second blowby gas pipe 23 includes a first end connected to thefirst oil separator chamber 6 of the internal combustion engine 1,wherein the first end is an upstream end in terms of a flow of blowbygas; and a second end connected to a section of the intake passage 11downstream of the throttle valve 14, specifically, connected to theintake collector 17, wherein the second end is a downstream end in termsof the flow of blowby gas. A PCV valve 26 is provided at a point ofconnection between the second blowby gas pipe 23 and the first oilseparator chamber 6, for mechanically adjusting a flow rate of blowbygas in accordance with a differential pressure. The PCV valve 26 alsoserves as a check valve to prevent a gas flow from the intake collector17 to the first oil separator chamber 6.

The engine controller 15 receives input of sensing signals from varioussensors and the like, wherein the sensors include: the air flow meter19; an accelerator opening sensor 31 for indicating an amount ofdepression of an accelerator pedal by a driver; a crank angle sensor 32for indicating a rotational speed of the internal combustion engine 1;an air fuel ratio sensor 33 for sensing an exhaust air fuel ratio in anexhaust passage not shown (oxygen sensor, or so-called wide-range airfuel ratio sensor); and a water temperature sensor 34 for indicating acooling water temperature.

The engine controller 15 performs various controls such as a control offuel injection quantity and timing by a fuel injection valve not shownof the internal combustion engine 1, a control of ignition timing by aspark plug not shown, a control of opening of the throttle valve 14, anda control of boost pressure by the turbocharger. In addition to thesecontrols, the engine controller 15 has various self-diagnosis functionsincluding a leak diagnosis for the blowby gas treatment device. Theengine controller 15 is connected to a warning light 35, and whendetermining as a result of the leak diagnosis that an out-of-system leakis present, activates the warning light 35.

The following describes a gas flow in the blowby gas treatment deviceconfigured as described above. Under a non-supercharging condition, thedownstream side of the throttle valve 14, namely, the inside of theintake collector 17 is subject to a negative pressure. Accordingly,fresh air flows from the intake passage 11 into the crank case 3 via thefresh air induction pipe 21, and thereby serves to ventilate the crankcase 3. The blowby gas in the crank case 3 flows into the first oilseparator chamber 6 as well as fresh air, and flows from the first oilseparator chamber 6 into the intake collector 17 via the second blowbygas pipe 23.

Under a supercharging condition, the intake collector 17, which isdownstream of the throttle valve 14, is subject to a positive pressure,so that it becomes impossible to treat blowby gas through the secondblowby gas pipe 23. Accordingly, under the supercharging condition, theopening of the pressure control valve 18 is controlled by the enginecontroller 15 to a suitable position, thereby causing a negativepressure in the region between the pressure control valve 18 and thecompressor 13. The negative pressure causes fresh air to flow from theintake passage 11 into the crank case 3 via the fresh air induction pipe21, and causes blowby gas in the crank case 3 to circulate from thefirst oil separator chamber 6 into the upstream side of the compressor13 via the first blowby gas pipe 22.

The following describes a leak diagnosis for detecting a leak in theblowby gas treatment device due to occurrence of a hole in the pipes 21,22, 23 or detachment of the pipes 21, 22, 23.

The present embodiment includes a leak diagnosis A performed under thenon-supercharging condition, and a leak diagnosis B started under thesupercharging condition. FIG. 2 is a flowchart showing a flow ofprocessing of the leak diagnosis A, and FIG. 5 is a flowchart showing aflow of processing of the leak diagnosis B. The leak diagnosis Aaccording to the present invention is an arbitrary diagnosis that isperformed additionally. Therefore, the following first describes theleak diagnosis B with reference to the flowchart of FIG. 5 .

The leak diagnosis B is performed at a suitable frequency, for example,once a trip. At Step 11, it is determined whether or not it is under thesupercharging condition. This determination may be based on the load androtational speed of the internal combustion engine 1, or may be based ondetermination by using the boost pressure sensor 20 whether or not theintake pressure is actually a positive pressure. When it is under thesupercharging condition, the process proceeds from Step 11 to Step 12.At Step 12, it is determined whether or not a diagnosis start conditionis satisfied. When the operating condition (load, rotational speed) ofthe internal combustion engine 1 or conditions such as the cooling watertemperature satisfies a specific condition, and the leak diagnosis B isnot yet performed during the current trip, the diagnosis start conditionis regarded as satisfied to permit the diagnosis to be started. Underthe diagnosis start condition, the throttle valve 14 is controlled tohave an opening suitable for generating a negative pressure downstreamof the throttle valve 14. When the answer to Step 12 becomes YES, theprocess proceeds to Step 13. At Step 13, a first stage diagnosis(corresponding to a first diagnosis recited in the claims) isimplemented by closing the shutoff valve 24 in the fresh air inductionpipe 21, and monitoring by the crank case pressure sensor 8 changes inpressure in the crank case 3 after the closing of the shutoff valve 24.

The fresh air induction pipe 21 is blocked by the shutoff valve 24, andthe negative pressure in the intake collector 17 is applied to theinside of the crank case 3 via the first blowby gas pipe 22, so that thepressure in the crank case 3 gradually falls when in normal state,namely, when no leak is present. With a leak, the pressure fallingbecomes insufficient. Incidentally, an inflow of fresh air through thesecond blowby gas pipe 23 (an inverse flow through the second blowby gaspipe 23) is prevented by the PCV valve 26. In FIG. 6 , a line L11indicates an example of pressure falling when in normal state, and aline L12 indicates an example of pressure falling when a leak ispresent. For distinguishing them from each other, a pressure value P2 isset as a suitable threshold value. The pressure value P2 may beconstant, or may be set variable in accordance with the operatingcondition (diagnosis start condition).

At Step 14, it is determined whether or not the pressure falls to thepressure value P2, at a time instant t2 in FIG. 6 , namely, a suitabledelay time after the closing of the shutoff valve 24. The delay time isseveral seconds in this example. When the answer to Step 14 is YES, theprocess proceeds to Step 15. At Step 15, it is determined that no leak(no leak to the outside of the system, and no leak within the system) ispresent, and the leak diagnosis B is terminated.

On the other hand, when the answer to Step 14 is NO, it means that thefirst stage diagnosis determines presence of an abnormality, and inorder to distinguish the out-of-system leak and the in-system leak fromeach other, a second stage diagnosis (corresponding to a seconddiagnosis recited in the claims) composed of Step 16 and the followingsteps is further performed. At Step 16, it is determined whether or nota condition for permitting the second stage diagnosis is satisfied. Thesecond stage diagnosis is performed under the non-superchargingcondition, specifically under an operating condition in which the intakeair quantity is allowed to rapidly decrease, preferably during fuel-cutoperation while the vehicle is decelerating with the accelerator openingbeing equal to zero. In this example, at Step 16, it is determinedwhether or not fuel-cut operation is being performed. In case where theinternal combustion engine 1 is of a hybrid electric vehicle andmotoring of the internal combustion engine 1 can be performed by anelectric motor, it is also preferable to perform the second stagediagnosis during motoring of the internal combustion engine 1.Incidentally, under the non-supercharging condition, the pressurecontrol valve 18 is fully opened basically.

When the second stage diagnosis is permitted at Step 16, the processproceeds to Step 17. At Step 17, the pressure control valve 18 iscontrolled continuously from a fully opened state into a fully closedstate, and at each state, a fully opened state intake air quantity(Qopen) and a fully closed state intake air quantity (Qclose) aremeasured by the air flow meter 19. Next, the process proceeds to Step18. At Step 18, it is determined whether or not the fully opened stateintake air quantity is equal to the fully closed state intake airquantity. This determination is substantially equal to determiningwhether or not the fully closed state intake air quantity is measured tobe less than the fully opened state intake air quantity. This comparisonin magnitude is given a suitable allowable error.

When the answer to Step 18 is YES, namely, when the fully opened stateintake air quantity is equal to the fully closed state intake airquantity, the process proceeds to Step 19. At Step 19, it is determinedthat a leak within the system of the blowby gas treatment device(namely, a failure such as a failure of valve operation or a failure ofsealing in the system), which is not an out-of-system leak, is present.In this situation, no blowby gas flows out to the external environment,and error information is stored in a memory of the engine controller 15without activation of the warning light 35.

When the answer to Step 18 is NO, namely, when it is determined at Step18 that the fully opened state intake air quantity and the fully closedstate intake air quantity are different from each other, the processproceeds to Step 20. At Step 20, it is determined that a leak to theoutside of the system of the blowby gas treatment device (occurrence ofa hole in piping or detachment of piping) is present. In this situation,the warning light 35 is activated for informing the driver.

The in-system leak is typically due to closed-state sticking of theone-way valve 25 in the first blowby gas pipe 22 (state where theone-way valve 25 cannot be opened sufficiently), or due to open-statesticking of the PCV valve 26 in the second blowby gas pipe 23 (statewhere the inverse flow cannot be prevented).

FIG. 8 shows a basic flow of gas (fresh air passing through the air flowmeter 19 and measured) when the pressure control valve 18 is fullyclosed. As indicated by a dotted arrow in FIG. 8 , when the pressurecontrol valve 18 is fully closed, the flow to the downstream side of thepressure control valve 18 in the intake passage 11 is blocked, and freshair flows via the fresh air induction pipe 21 into the second oilseparator chamber 7, and flows along a shortcut path in the crank case3, and returns from the first oil separator chamber 6 into the intakepassage 11 (the downstream side of the pressure control valve 18) viathe first blowby gas pipe 22. Accordingly, on the assumption that therotational speed of the internal combustion engine 1 is constant, thefully opened state intake air quantity and the fully closed state intakeair quantity, which are measured by the air flow meter 19, are equal toeach other.

In other words, without a leak to the outside of the system such as aleak due to occurrence of a hole, both when the pressure control valve18 is in the fully opened state and when the pressure control valve 18is in the fully closed state, all of the fresh air flowing into thecombustion chambers 2 passes through the air flow meter 19 and isthereby measured by the air flow meter 19, so that the fully closedstate intake air quantity is unchanged with respect to the fully openedstate intake air quantity.

In contrast, with occurrence of a hole in any one of the pipes, thenegative pressure occurring downstream of the throttle valve 14 causesoutside air to inflow via the hole and be finally induced into thecombustion chambers 2. The outside air inflowing via the hole does notpass through the air flow meter 19, and is not measured by the air flowmeter 19. As the fully opened state of the pressure control valve 18 iscompared with the fully closed state of the pressure control valve 18,as shown in FIG. 8 , the proportion of intake air quantity added via thehole in the pipe is larger when the pressure control valve 18 is in thefully closed state, so that the fully closed state intake air quantitymeasured by the air flow meter 19 is smaller than the fully opened stateintake air quantity. Therefore, by performing the second stage diagnosisin addition to the first stage diagnosis, it is possible to reliablyidentify a leak to the outside of the system.

FIG. 7 shows a relationship between a ratio (Qclose/Qopen) between thefully opened state intake air quantity (Qopen) and the fully closedstate intake air quantity (Qclose) and an equivalent diameter of theopening of a hole in piping. Without an out-of-system leak such as onedue to occurrence of a hole, the ratio (Qclose/Qopen) is maintained at 1as indicated by a line L13. With occurrence of a hole in piping, theratio (Qclose/Qopen) becomes equal to a value smaller than 1 asindicated by a line L14, wherein the value decreases as the equivalentdiameter increases. Accordingly, a threshold value is set as indicatedby a line L15 in accordance with a setpoint of the equivalent diameter,wherein based on the threshold value, a leak to the outside of thesystem is identified.

On the other hand, with closed-state sticking of the one-way valve 25 inthe first blowby gas pipe 22, during the first stage diagnosis, thenegative pressure occurring downstream of the pressure control valve 18is not applied to the inside of the crank case 3, and the pressurefalling becomes insufficient, so that the answer to Step 14 isdetermined as NO (abnormal). However, during the second state diagnosis,fresh air does not return via the first blowby gas pipe 22 to the intakepassage 11, but returns to the intake collector 17 via the second blowbygas pipe 23. Therefore, the fully opened state intake air quantity andthe fully closed state intake air quantity are measured to besubstantially equal to each other.

Similarly, in case of open-state sticking of the PCV valve 26, thesecond blowby gas pipe 23 is in a state allowing communication, so thatthe first stage diagnosis determines the pressure fall as insufficient,and the answer to Step 14 becomes NO (abnormal). However, during thesecond stage diagnosis, there is no gas movement between the system andthe external environment, so that the fully opened state intake airquantity and the fully closed state intake air quantity are calculatedas substantially equal to each other.

In the foregoing embodiment, when the presence of an abnormality isdetermined by the first stage diagnosis (No at Step 14), the processproceeds to the second stage diagnosis. However, the first stagediagnosis and the second stage diagnosis may be performed individuallyfrom each other, and thereafter the results of both may be combined toobtain a similar final result of diagnosis.

Furthermore, the sensing of the fully opened state intake air quantityand the sensing of the fully closed state intake air quantity are notlimited to the process where they are performed in succession. Forexample, the sensing of the fully opened state intake air quantity andthe sensing of the fully closed state intake air quantity may beperformed individually in respective suitable timings.

Furthermore, in the foregoing embodiment, the second stage diagnosis isperformed with the pressure control valve controlled to be in the fullyopened state. However, it is unnecessary to control the pressure controlvalve into the fully opened state. The second stage diagnosis may beimplemented by controlling the pressure control valve into an open-sidestate (state where the valve opening is closer to the fully openedside), and using an open-side state intake air quantity measured whenthe pressure control valve is in the open-side state. Moreover, in theforegoing embodiment, the second stage diagnosis is performed with thepressure control valve controlled to be in the fully closed state.However, it is unnecessary to control the pressure control valve intothe fully closed state. The second stage diagnosis may be implemented bycontrolling the pressure control valve into a closed-side state (statewhere the valve opening is closer to the fully closed side), and using aclosed-side state intake air quantity measured when the pressure controlvalve is in the closed-side state.

Next, the following describes the processing of the leak diagnosis Awith reference to the flowchart of FIG. 2 , wherein the leak diagnosis Ais performed additionally.

The leak diagnosis A is performed at a suitable frequency, for example,once a trip. At Step 1, it is determined whether or not it is under thenon-supercharging condition. This determination may be based on the loadand rotational speed of the internal combustion engine 1, or may bebased on determination by using the boost pressure sensor 20 whether ornot the intake pressure is actually a negative pressure. When it isunder the non-supercharging condition, the process proceeds from Step 1to Step 2. At Step 2, it is determined whether or not a diagnosis startcondition is satisfied. When the operating condition (load, rotationalspeed) of the internal combustion engine 1 or conditions such as thecooling water temperature satisfies a specific condition, and the leakdiagnosis A is not yet performed during the current trip, the diagnosisstart condition is regarded as satisfied to permit the diagnosis to bestarted. Under the diagnosis start condition, the throttle valve 14 hasan opening suitable for generating a negative pressure downstream of thethrottle valve 14. When the answer to Step 2 becomes YES, the processproceeds to Step 3. At Step 3, a first stage diagnosis is implemented byclosing the shutoff valve 24 in the fresh air induction pipe 21, andmonitoring by the crank case pressure sensor 8 changes in pressure inthe crank case 3 after the closing of the shutoff valve 24.

The fresh air induction pipe 21 is blocked by the shutoff valve 24, andthe negative pressure in the intake collector 17 is applied to theinside of the crank case 3 via the second blowby gas pipe 23, so thatthe pressure in the crank case 3 gradually falls when in normal state,namely, when no leak is present. With a leak, the pressure fallingbecomes insufficient. Incidentally, an inflow of fresh air through thefirst blowby gas pipe 22 (an inverse flow through the first blowby gaspipe 22) is prevented by the one-way valve 25. In FIG. 3 , a line L1indicates an example of pressure falling when in normal state, and aline L2 indicates an example of pressure falling when a leak is present.For distinguishing them from each other, a pressure value P1 is set as asuitable threshold value. The pressure value P1 may be constant, or maybe set variable in accordance with the operating condition (diagnosisstart condition).

At Step 4, it is determined whether or not the pressure falls to thepressure value P1, at a time instant t1 in FIG. 3 , namely, a suitabledelay time after the closing of the shutoff valve 24. The delay time isseveral seconds in this example. When the answer to Step 4 is YES, theprocess proceeds to Step 5. At Step 5, it is determined that no leak (noleak to the outside of the system, and no leak within the system) ispresent, and the leak diagnosis A is terminated.

On the other hand, when the answer to Step 4 is NO, it means that thefirst stage diagnosis determines presence of an abnormality, and inorder to distinguish the out-of-system leak and the in-system leak fromeach other, a second stage diagnosis composed of Step 6 and thefollowing steps is further performed. In the shown example, since thesecond stage diagnosis is performed subsequent to the first stagediagnosis, the operating condition of the internal combustion engine 1is under the non-supercharging condition.

At Step 6, it is determined whether or not the intake air quantitymeasured by the air flow meter 19 (namely, the sensed intake airquantity) is equal to an actual intake air quantity flowing into thecylinders of the internal combustion engine 1. This comparison is givena suitable allowable error. In this example, this is implemented bydetermining whether or not a quantity of increasing correction appliedto a basic fuel injection quantity based on the sensed intake airquantity is greater than or equal to a predetermined level under afeedback control of air fuel ratio based on the air fuel ratio sensor33.

As is known by the skilled person, in an air fuel feedback control witha target air fuel ratio set to a theoretical air fuel ratio point, theinjection quantity injected by the fuel injection valve (specifically,the width of injection pulsing applied to the fuel injection valve) Tiis calculated by the following mathematical expression using the basicfuel injection quantity Tp that is calculated from the sensed intake airquantity and the engine rotational speed.Ti=Tp·(α+αm)·K+Ts

where α represents a feedback correction coefficient that is calculatedin succession by PID control or the like for convergence to the targetair fuel ratio with reference to the sensing signal of the air fuelratio sensor 33; am represents a correction coefficient learning valuethat is calculated based on a bias of the feedback correctioncoefficient α for correspondence to an individual deviation and a timelychange, wherein the correction coefficient learning value is allocatedto a map defined by load and rotational speed as parameters, and islearned and updated; K represents an increasing correction coefficientsuch as one relating to the cooling water temperature; and Ts representsa voltage correction component corresponding to a response delay of thefuel injection valve.

Accordingly, the sum (α+αm) of the feedback correction coefficient α andthe correction coefficient learning value am in the mathematicalexpression corresponds to the quantity of increasing correction appliedto the basic fuel injection quantity Tp. As detailed below, when anout-of-system leak is present due to occurrence of a hole in piping anddetachment of piping, the actual intake air quantity flowing into thecylinders becomes larger than the sensed intake air quantity measured bythe air flow meter 19. In other words, the sensed intake air quantity ismeasured to be smaller than actual. This causes that during the air fuelratio feedback control, a control based on the basic fuel injectionquantity Tp based on the sensed intake air quantity causes the air fuelratio to be leaner than the target air fuel ratio (for example,theoretical air fuel ratio). Therefore, the correction quantity (α+αm)is set large. At Step 6, when the correction quantity (α+αm) is smallerthan a predetermined value, the answer is YES, namely, it is determinedthat the sensed intake air quantity is equal to the actual intake airquantity. When the correction quantity (α+αm) is larger than or equal tothe predetermined value, the answer is NO, namely, it is determined thatthe actual intake air quantity is larger than the sensed intake airquantity.

When the answer to Step 6 is YES, namely, when it is determined at Step6 that the sensed intake air quantity is equal to the actual intake airquantity, the process proceeds to Step 7. At Step 7, it is determinedthat a leak within the system of the blowby gas treatment device(namely, a failure such as a failure of valve operation or a failure ofsealing in the system) is present. In this situation, no blowby gasflows out to the external environment, and error information is storedin a memory of the engine controller 15 without activation of thewarning light 35.

When the answer to Step 6 is NO, namely, when it is determined at Step 6that the actual intake air quantity is larger than the sensed intake airquantity, the process proceeds to Step 8. At Step 8, it is determinedthat a leak to the outside of the system of the blowby gas treatmentdevice (occurrence of a hole in piping or detachment of piping) ispresent. In this situation, the warning light 35 is activated forinforming the driver.

The in-system leak is typically due to open-state sticking of theone-way valve 25 in the first blowby gas pipe 22 (state where theinverse flow cannot be prevented).

During the first stage diagnosis, the pressure in the crank case 3gradually falls, as the fresh air induction pipe 21 is blocked by theshutoff valve 24 and a negative pressure is applied to the intakecollector 17 via the second blowby gas pipe 23. When the one-way valve25 is stuck in the open state, fresh air flows from the intake passage11 into the crank case 3 via the first blowby gas pipe 22, so that thepressure falling in the crank case 3 becomes insufficient. Accordingly,the first stage diagnosis (Step 4) determines presence of anabnormality.

However, even when the one-way valve 25 is stuck in the open state,fresh air flowing from the first blowby gas pipe 22 into the first oilseparator chamber 6 flows into the intake collector 17 via the secondblowby gas pipe 23, and is finally supplied to the combustion chambers2. The fresh air flowing through the second blowby gas pipe 23 passesthrough the air flow meter 19, and is thereby measured as a part of theintake air quantity by the air flow meter 19. Therefore, even when theone-way valve 25 is stuck in the open state, the sensed intake airquantity measured by the air flow meter 19 is basically equal to theactual intake air quantity flowing into the cylinders of the internalcombustion engine 1.

In other words, without an out-of-system leak such as one due tooccurrence of a hole, even with an in-system leak such as one due toopen-state sticking of the one-way valve 25, all of the fresh airflowing into the combustion chambers 2 passes through the air flow meter19 and is measured by the air flow meter 19, so that the actual intakeair quantity does not deviate significantly from the sensed intake airquantity.

In contrast, with occurrence of a hole in any one of the pipes, thenegative pressure occurring downstream of the throttle valve 14 causesoutside air to inflow via the hole and be finally induced into thecombustion chambers 2. The outside air inflowing via the hole does notpass through the air flow meter 19, and is not measured by the air flowmeter 19. Accordingly, as compared with the actual intake air quantityflowing into the cylinders of the internal combustion engine 1, thesensed intake air quantity measured by the air flow meter 19 becomesrelatively small. Therefore, by performing the second stage diagnosis inaddition to the first stage diagnosis, it is possible to reliablyidentify a leak to the outside of the system.

FIG. 4 shows a relationship between a ratio (Qafm/Qcylin) between thesensed intake air quantity (Qafm) and the actual intake air quantity(Qcylin) and an equivalent diameter of the opening of a hole in piping.Without an out-of-system leak such as one due to occurrence of a hole,the ratio (Qafm/Qcylin) is maintained at 1 as indicated by a line L3.With occurrence of a hole in piping, the ratio (Qafm/Qcylin) becomesequal to a value smaller than 1 as indicated by a line L4, wherein thevalue decreases as the equivalent diameter increases. Accordingly, athreshold value is set as indicated by a line L5 in accordance with asetpoint of the equivalent diameter, wherein based on the thresholdvalue, a leak to the outside of the system is identified.

During the leak diagnosis A shown in FIG. 2 , when the presence of anabnormality is determined by the first stage diagnosis (No at Step 4),the process proceeds to the second stage diagnosis. However, the firststage diagnosis and the second stage diagnosis may be performedindividually from each other, and thereafter the results of both may becombined to obtain a similar final result of diagnosis.

Although the comparison at Step 6 between the sensed intake air quantityand the actual intake air quantity is based on the correction quantity(α+αm) of the air fuel ratio feedback control in the foregoing example,the actual intake air quantity may be calculated based on the sensedvalue of the boost pressure sensor 20 at the intake collector 17, andcompared with the sensed intake air quantity.

In the foregoing embodiment, the leak diagnosis A is performed under thenon-supercharging condition and the leak diagnosis B is performed suchthat the first stage diagnosis is performed under the superchargingcondition and thereafter the second stage diagnosis is performed underthe non-supercharging condition (preferably, during fuel cut operationor during motoring).

The present embodiment where the leak diagnosis A and the leak diagnosisB are both performed serves to enhance the accuracy of the leakdiagnosis and reduce the frequency of incorrect determination. Asrequired, it may be implemented by appropriately combining the result ofthe leak diagnosis A and the result of the leak diagnosis B.

For example, at Step 5 in the leak diagnosis A (presence of no leak isdetermined), it is possible to determine no occurrence of a hole in apipe system including at least the fresh air induction pipe 21 and thesecond blowby gas pipe 23, whereas at Step 15 in the leak diagnosis B,it is possible to determine no occurrence of a hole in a pipe systemincluding at least the fresh air induction pipe 21 and the first blowbygas pipe 22. Furthermore, open-state sticking of the one-way valve 25can be detected by the leak diagnosis A, whereas closed-state stickingof the one-way valve 25 can be detected by the leak diagnosis B.

The invention claimed is:
 1. A leak diagnosis method for a blowby gastreatment device of an internal combustion engine, wherein the blowbygas treatment device includes: a fresh air induction pipe structured toinduce fresh air into a crank case from a section of an intake passagedownstream of an air flow meter; a pressure control valve disposed in asection of the intake passage upstream of a throttle valve and upstreamof a compressor; a first blowby gas pipe structured to induce blowby gasfrom the crank case into a section of the intake passage between thecompressor and the pressure control valve; a second blowby gas pipestructured to induce blowby gas from the crank case into a section ofthe intake passage downstream of the compressor and downstream of thethrottle valve; a shutoff valve structured to block the fresh airinduction pipe; a one-way valve structured to allow only a gas flow inthe first blowby gas pipe from the crank case to the intake passage; anda PCV valve disposed in the second blowby gas pipe; the leak diagnosismethod comprising: performing a first diagnosis to close the shutoffvalve under a supercharging condition and determine whether falling of apressure in the crank case after the closing of the shutoff valve isnormal or abnormal; performing a second diagnosis to control thepressure control valve into an open-side state and a closed-side stateunder a non-supercharging condition and determine whether or not anopen-side state intake air quantity is equal to a closed-side stateintake air quantity, wherein the open-side state intake air quantity isa quantity of intake air measured when the pressure control valve is inthe open-side state, and wherein the closed-side state intake airquantity is a quantity of intake air measured when the pressure controlvalve is in the closed-side state; determining presence of a leak to anoutside of a system of the blowby gas treatment device, in response to acondition that the first diagnosis determines the falling of thepressure as abnormal and the second diagnosis determines the open-sidestate intake air quantity as unequal to the closed-side state intake airquantity; and determining presence of a failure within the system of theblowby gas treatment device, in response to a condition that the firstdiagnosis determines the falling of the pressure as abnormal and thesecond diagnosis determines the open-side state intake air quantity asequal to the closed-side state intake air quantity.
 2. The leakdiagnosis method as claimed in claim 1, comprising: performing the firstdiagnosis prior to the second diagnosis; and performing the seconddiagnosis subsequent to a determination by the first diagnosis that thefalling of the pressure is abnormal.
 3. The leak diagnosis method asclaimed in claim 1, wherein the second diagnosis is implemented bycontrolling the pressure control valve continuously from the open-sidestate to the closed-side state, and measuring the open-side state intakeair quantity and the closed-side state intake air quantity in eachstate.
 4. The leak diagnosis method as claimed in claim 1, wherein thesecond diagnosis is performed during fuel cut operation under vehicledeceleration or during motoring by an external driving effort.
 5. Theleak diagnosis method as claimed in claim 1, comprising: determining thefailure within the system as a failure due to closed-state sticking ofthe one-way valve or open-state sticking of the PCV valve.
 6. The leakdiagnosis method as claimed in claim 1, comprising: activating a warninglight in response to a determination of presence of a leak to theoutside of the system of the blowby gas treatment device; andinactivating the warning light in response to a determination ofpresence of a failure within the system of the blowby gas treatmentdevice.
 7. The leak diagnosis method as claimed in claim 1, comprising:implementing the second diagnosis by controlling the pressure controlvalve into a fully opened state and a fully closed state under thenon-supercharging condition and determine whether or not a fully openedstate intake air quantity is equal to a fully closed state intake airquantity, wherein the fully opened state intake air quantity is aquantity of intake air measured when the pressure control valve is inthe fully open state, and wherein the fully closed state intake airquantity is a quantity of intake air measured when the pressure controlvalve is in the fully closed state; determining presence of a leak tothe outside of the system of the blowby gas treatment device, inresponse to a condition that the first diagnosis determines the fallingof the pressure as abnormal and the second diagnosis determines thefully opened state intake air quantity as unequal to the fully closedstate intake air quantity; and determining presence of a failure withinthe system of the blowby gas treatment device, in response to acondition that the first diagnosis determines the falling of thepressure as abnormal and the second diagnosis determines the fullyopened state intake air quantity as equal to the fully closed stateintake air quantity.
 8. An internal combustion engine blowby gastreatment device leak diagnosis device comprising: an internalcombustion engine including a compressor in an intake passage forsupercharging; a blowby gas treatment device including: a fresh airinduction pipe structured to induce fresh air into a crank case from asection of the intake passage downstream of an air flow meter; apressure control valve disposed in a section of the intake passageupstream of a throttle valve and upstream of the compressor; a firstblowby gas pipe structured to induce blowby gas from the crank case intoa section of the intake passage between the compressor and the pressurecontrol valve; a second blowby gas pipe structured to induce blowby gasfrom the crank case into a section of the intake passage downstream ofthe compressor and downstream of the throttle valve; a shutoff valvestructured to block the fresh air induction pipe; a one-way valvestructured to allow only a gas flow in the first blowby gas pipe fromthe crank case to the intake passage; and a PCV valve disposed in thesecond blowby gas pipe; and a control section configured to diagnoseleaking of the blowby gas treatment device, wherein the control sectionis configured to: perform a first diagnosis to close the shutoff valveunder a supercharging condition and determine whether falling of apressure in the crank case after the closing of the shutoff valve isnormal or abnormal; perform a second diagnosis to control the pressurecontrol valve into an open-side state and a closed-side state under anon-supercharging condition and determine whether or not an open-sidestate intake air quantity is equal to a closed-side state intake airquantity, wherein the open-side state intake air quantity is a quantityof intake air measured when the pressure control valve is in theopen-side state, and wherein the closed-side state intake air quantityis a quantity of intake air measured when the pressure control valve isin the closed-side state; determine presence of a leak to an outside ofa system of the blowby gas treatment device, in response to a conditionthat the first diagnosis determines the falling of the pressure asabnormal and the second diagnosis determines the open-side state intakeair quantity as unequal to the closed-side state intake air quantity;and determine presence of a failure within the system of the blowby gastreatment device, in response to a condition that the first diagnosisdetermines the falling of the pressure as abnormal and the seconddiagnosis determines the open-side state intake air quantity as equal tothe closed-side state intake air quantity.